how to make an icicle starts with an
argument for why to make an icicle.

we like icicles because they accurately
portray environmental conditions in an understated manner. you can
make people think "cold" and "snow" by going the obvious way and making
whole drifts out of batting, or you can build a subtle, and sometimes more
believable scene, by making a rock and some dirt and adding "cold" details.
a rift of "snow" drifted in beside a cleft in your fake rock suggests wind
and cold without the actual snow and without the high maintenance factor of
keeping mounds of "snow" from yellowing or getting dusty. a rift of
"snow" and an icicle hanging from driftwood or wire is a great frigid touch.

however, when a white base is desired or
required, icicles are the most convincing detail to add to your
batting/artificial snow base. the contrast of clear and hard texture
against the fluffiness of the snow is very convincing.

tear off a piece of
batting and twist it to approximate the size and shape of an icicle
(something longish, and wider at the top than at the bottom).

spoon resin over batting with popsicle stick until enough
resin clings to batting to make it sticky and drippy. wrap the dry
part of the batting that you're holding onto with your fingers over the wire
and down, letting the dry part drift down into the wet resin and glue
itself. you've made a "loop" at the top that will hang on the wire,
and with which you can attach your icicle to your habitat later.

continue spooning resin over icicle, either until it looks
like you want it to or you run out of working time and the resin sets.

let icicle set. if longer icicle is
desired, fresh resin can be mixed and poured over basic icicle until the
suitable dimensions are achieved.

attach icicle to habitat with super-glue or hot glue. leave the fuzzy
batting loop on if you are attaching it to a snowy limb. dust
artificial snow over transition. trim fuzzy batting loop off if a
harder look is desired.

habitat hint:
in real life, gravity, water, and cold air make icicles. to make your
icicles look best, be sure to hang them pointing straight down, as if they
actually froze in place while the water was dripping straight down toward
the ground. wildly-angled icicles aren't so convincing.